Patent Literature 1 is an example of technical literature of this field. Patent Literature 1 discloses a valve timing control device that is provided in a cylinder of an internal combustion engine so as to control the driving timing of an intake/exhaust value. In the valve timing control device, the lower the voltage of a power source is, the earlier the energization of an electromagnetic actuator for holding the intake/exhaust valve starts to thereby prevent a delay of activation of the electromagnetic actuator due to a decrease in the voltage of the power source.